Synchronous alternating current machine for low and for variable speed



May s, 193e. J. LELL 2,039,322

SYNCHRONOUS ALTERNIATTI-NG CURRENT MACHINE FOR LOW AND FOR VARIABLE SPEED www May 5, 1935 J. LELL' 2,039,322

SYNCHRONOUS ALTERNATING CURRENT MACHINE FOR LOW AND FOR VARIABLE. SPEED Filed Dc. 50, 1955 2 sheets-sheet 2 Patented May 5, 1936 PATENT OFFICE S YNCHBONOUS ALTERNATING CURRENT MACHINE. FOR LOW AND FOR VARIABLE SPEED Jacob Lell, Heidenheim-on-the-Brenz, Germany Application December 30, 1933, Serial No. 704,728

InG

ermany December 31, 1932 5 Claims. (Cl. 172-120) This invention relates to alternating current machines having synchronous characteristics and designed particularly 4for use under conditions requiring operation at relatively low and/or variable speeds.

The principles underlying the present invention are applicable to either alternating current generators or motors, and when applied to alternating current generation, it is possible to maintain substantially constant frequency irrespective of variations in speed of the prime mover, and when applied to alternating current motors, it is posgsible to maintain synchronous operation of the motor throughout a wide range of speed.

Alternating current machines are known which may be coupled to high speed prime movers and which, for this purpose, are provided with squirrel-cage rotors. These machines, however," are not desirable where al constant frequency is essential inasmuch as they are unable to maintain constant frequency in the generated potential during variations of speed of the prime mover.

"lhere are also known alternating current ma` chines in which the stator and rotor revolve in opposite directions so that when both revolve at the same speed, the resulting frequency in the generated potential is twice as high as if only the rotor revolved in a stationary stator. 'Such machines have'the advantage of reducing the number of poles, weight of the rotating parts, and being smaller in dimensions, offer an increased security against detrimental centrifugal forces in the rotating masses. However, machines of. this type possess certain undesirable characteristics such as the necessity to pass the Whole power through the slip rings and their inability to follow accurately the varying speed of the prime mover. With these facts in mind my invention comprehends a rotary machine operating under the well known principles characterizing synchronous machines, but which permit such machine when operating as a motor to run at varying speeds throughout a wide range and when operating as a generator to generate a current having substantially constant frequency in spite of substantially wide fluctuations in speed of the prime mover.

The invention consists of certain novel features of construction and combination of parts described in the following specification and pointed out more clearly in the appended claims, and I have illustrated in the accompanying drawings a preferred embodiment oi my invention, the novel features of which have been set forth more clearly in the appended claims.

Referring to the drawings:

Figure 1 is a schematic diagram of the windings of my machine.

Figure 2 is a plan view, partly in section, of a preferred form of my invention.

Referring to Fig. 2 of the drawings, wherein I have shown a preferred embodiment of .my invention, I have shown a main and an auxiliary machine, the rotating parts of which are connected together by an element indicated by the reference character I0. The element I is provided with a shaft I mounted in suitable bearings I2 and is arranged to carry on its surface an armature winding I4 anda eld winding I3. The eld winding I3 is operatively associated with a stator element 9 provided with a conventional three phase ring winding, whereas the armature element III. is operatively associated with a relan tively rotatable field winding II. The field winding II may be provided with any suitable number of poles IIa which may be supplied in any suitable manner with direct current of desirable potential through slip rings SI-S2. The shaft I is provided with a suitable driving gear 3 secured thereto, whereas the eld element II is provided with a driving gear I5. The gear elements 3 and I5 are designed to be driven respectively by gears 4 and 2 connected to a suitable variable speed transmission l, the latter being operatively connected to a motor 8 by means of a coupling element 5. 'I'he gear 2 and its cooperating gear I5 are provided with oblique or spiral tee'th permitting slight axial movement of the gear 2 on its shaft I6 by means of the pin and slot connection shown in Fig. 2. The purpose of this axial movement of the gear 2 will be presently explained.

'I'he variable speed transmission device I may be of conventional design permitting various relative speeds of the gears 2 and 4, and the coupling device 5 is preferably arranged in a manner such that when open the shaft 6 of the motor may drive the shaft I6 through the transmission device l.

. When the coupling member 5 is closed the gear l is operatively connected to the transmission device 1 through the pin and slot connection between the right hand member of the coupling 5';

asshown in Fig. 2.

The windings I3 and I4 on the rotating element I0 are clearly indicated schematically in Fig. 1. 'I'he winding I4 functions as the armature winding for the auxiliary machine comprising the ileld poles N and the armature I4. The armature winding I4 comprises six p'oles, corresponding in number to the poles N of the rotating neld II. As shown in Fig. 1, each pole comprises six coils, it being noted that the cor responding coils of each pole are connected to bus bars S, there being twice as many bus bars as there are coils per pole, so that corresponding coils of each pole may be connected, respectively, to the same pair of bus bars. Thus, as seen in Fig. 1, the coils comprising the wires numbered I and I in each pole are connected to the same pair of bus bars, it being noted that the connections between said coils and the bus bars are reversed in accordance with the polarity of the poles, so that the effective E. M. F.s induced in said coils are parallelly connected to the respective pairs of bus bars.

The field winding I3 comprises but a single pair of poles as shown in Fig. l, each pole having six coils, two coils of each pole being connected to l each pair of bus bars, as shown. It is to be noted, also. that the armature winding I4 progresses in one direction, whereas the field winding I3 progresses in the opposite direction with reference to the element I0 on which they are both mounted.

Considering the construction. shown in Fig. 2, it is apparent that with the movable field element I I energized by a suitable source of direct current, and assuming there are the same number of poles in the field winding I3 as there are in the windings II and I4, the currents induced in the armature I4 and conductively communicated to the fielld I3 will lrotate in the opposite direction and at the same speed as the speed of the rotating field element II. The reversal in direction is caused by the opposite direction of progression of the windings I4 and I3, respectively.

Similarly, if the field element II is held fixed and the rotor III turned in a direction opposite to` that assumed in the preceding example, the currents induced in the held winding I3 will rotate in the same direction as the element III, but at twice the speed thereof.

With the arrangement of poles shown in the drawings, namely, six poles on the field element I I and in the armature I4 and only two poles in the field element I3, there will be a corresponding multiplication of speed between the rotating elements I I and IIJ and the resulting rotating field I3. In general, with the winding I3 reversed with reference to that of the armature I4, as shown, and simultaneous rotation of the iield element II of the rotor III, the rotary speed of the field I3 will be twice that of the rotor plus that of the pole wheel, Thus, if conditions are selected such that the additive magnetic field speed (double the rotor speed plus the rotary field element speed) is synchronous with the stator rotary field, then upon change of the pole wheel speed the rotor speed will change in such manner as to retain synchronism between the magnetic field set up in the rotary element I0 and the stator rotary field, as in conventional and well known alternating current machines.

If we assume the field element I I to be rotated in a clockwise direction and the rotor III to be rotated in a counter-clockwise direction at the same speeds, then the magnetic vfield I3 would rotate three times as fast as the rotor if thirtysix coils were present in the magnetic field, but since, instead of thirty-six coils, there are only twelve coils on the magnetic field shown in the drawings, the speed of the latter is tripled, i. e., it rotates under the above-mentioned conditions nine times as fast as the rotary field element II or the rotor Il. It, as a result of regulation the rotary field element II turns faster or slower than the rotor I0, the condition always obtains `that the rotating magnetic field speed is equal to three times the sum of the rotor speed and rotating field element speed.

In operation, the apparatus shown in Fig. 2 may be stated as follows:

Considering the stator winding 9 disconnected from its energizing potential and the rotor III and the field element II stationary, the coupling 5 is opened so that the motor 3 may drive straight through to the shaft I6 with thegear 2 splined thereon. The motor 8 is then energized and the field element I I driven at a speed in synchronism with the energizing current of the stator 9. This speed may be attained through proper regulation of the transmission device l. As soon as the element II has reached synchronous speed as stated, the stator 9 is energized, this being effected without any disturbancedue to phase displacement between the prevailing currents inasmuch as the oblique gear teeth on thc gears 2 and I5 and permissible axial movement of the gear 2 allows the rotor I0 to assume its proper angular position with reference to the rotating field set up in the stator 9 smoothly and without electrical or mechanical disturbance. Under these conditions there is no tendency for the rotor I0 to rotate. This tendency only arises when a relative phase displacement is produced in the line of force between the magnetic field I 3 and the stator rotary field. This may be effected by an'axial displacement of the gear 2 on the shaft' I6 (by any suitable means not shown),

' and a change in the transmission ratio of the drive mechanism 1. 'I'he transmission device 1 is then regulated to cause decreasing speed of the eld'element II until the rotary speed of the gear 4 is substantially equal to that of the motor 3. The motor 3 may now be cut out and the coupling element 5 closed and the machine continues to run like a normal synchronous machine. The speedof the rotor may now be regulated within relatively wide ranges by adjusting the transmission mechanism to change the speed ratio between gears 2 and 4, and this without altering the synchronous relation between the magnetic eld I3 and the field of the stator 3.

It is thus apparent that the main machine comprising the stator 3 and the field winding i3 is associated with the auxiliary machine coniprislng the rotating pole clement I I and the armature Winding I4 in a manner such that the rotor I0 functions to simultaneously carry the armature winding I4 in operative relation with reference to the pole elements I0 and the field winding I3 in operative relation with respect to the stator winding 3. Furthermore, when the machine is in operation, the rotor I0 operating through the gear wheels 3 and 4 and the transmission device 1, functions to drive the pole element II at varying speeds with reference thereto for the purpose of varying the speed of the element I0 without destroying the synchronous operation thereof with reference to the stator element 9.

armature and eld windings, and auxiliary maf chine including armature and field windings, a rotary drum member common to both machines, the armature of the auxiliary machine and the iield of the main machine being wound upon said drum member for rotation therewith as a unit with respect to the iield of the auxiliary machine and the armature of the main machine, respectively, and conductor means connecting like pole portions of theauxiliary armature winding and the main eld winding.

2. The machine described in claim 1 characterized by the fact that the direction of progression of the iieid winding of the main machine is the reverse oi that of the armature winding of the auxiliary machine with which it is connected.

3. The machine described in claim 1 characterized by power transmission means interconnecting said drum member and the iield member o! the auxiliary machine for positively rotating the eld winding of the auxiliary machine from said drum member and in the opposite direction.

4. The machine described in claim 1 characterized by means for driving the neld of the auxiliary machine from the armature of the auxiliary machine by a variable speed gearing, and means for iixing said variable speed gearing to provide any desired speed transformation between the driving and driven elements thereof.

5. The machine described in claim 1 characterized by variable speed gear mechanism directly connected between the armature of the auxiliary machine and the eld of the auxiliary machine for driving the eld from the armature, and means for relatively Varying the phase relation oi' the field with respect to the armature while maintaining the relative speed thereof constant.

JACOB LEIL. 

